Apparatus for electrolytic surface coating of pourable material

ABSTRACT

The bulk material is transportable in an electrolyte in the conveying trough of a vibrator conveyor. The conveying trough forms a cathodic track for the bulk material. According to the invention, a granulate anode (40) is provided which consists of a granulate of the material provided for deposition, which is transportable with the vibration in an anodic track (44) associated with the cathodic track (22). This form of realization of the apparatus with a large-surface anode of movable granulate results in a simple design solution for supplying and for replacing the anodes and in a better material utilization of the anode. In addition, the necessary down times are reduced.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for electrolytic surface coatingof pourable material, preferably for electrodeposition of metal, inparticular aluminum, from an electrolyte. The pourable material istransported in the cathodic track of a vibrator conveyor at least partlyin the treatment bath of the electrolyte.

It is known that by surface improvement of metal parts their life can belengthened and new areas of use can be opened up. For example, thecoating of light metal and ferrous materials may be appropriate, as theygenerally involve relatively base metals, the surfaces of which maycorrode under atmospheric action. Suitable pretreatment gives the partsa polished surface without cover layer. The metallic coating may besupplemented with an aftertreatment.

During the electrodeposition the pourable small parts must be heldtogether so that each individual part has electric contact. On the otherhand, the bulk material to be treated should be spread out to the extentthat the metal deposition can occur on a product surface as large aspossible and a current density as uniform as possible is ensured on allparts. Another essential prerequisite for satisfactory metal coatingswith a uniform layer thickness is sufficient mixing of the materialduring the electrodeposition. The apparatus for electrolytic surfacecoating is equipped with conveying means for the transport of the bulkmaterial through the electrolyte, which in conjunction withcorresponding inlet and outlet locks permit either continuous orintermittent feeding and removal of the material. In addition, themovement through the electrolyte and the thorough mixing of the materialas well as the transport through the electrolyte must be carried out insuch a way that gentle treatment of the material is ensured and evendelicate parts are not mechanically damaged during theelectrodeposition.

For mass electrodeposition, in particular for electrodeposition ofaluminum, a known apparatus is suitable in which a vibrator conveyorwith a horizontal and a vertical vibration component is provided for thetransport of the pourable material through the treatment bath. Thisvibrator conveyor transports the pourable material, utilizing the forcesof gravity, in a spiral conveying trough in ascending direction around acentral pipe connected with the conveying trough. The vibrator conveyoris accommodated with the central pipe in a gasproof vessel whichcontains an electrolyte into which the vibrator conveyor dips partially.As drive means are used for example oblique-action vibrators orobliquely set rods. Such vibrator conveyers require relatively littledrive force and make possible a gentle conveyance of the pourablematerial. One obtains intensive product movement and good electrolyteexchange as well as uniform current consumption over the entireeffective surface of the spread-out material (EP-A0 209 015).

In a known apparatus for the plating of parts by immersion and movementin a plating solution, these parts execute a vibrational movement and atthe same time a circular movement. The parts are present with theplating solution in a vessel. The movement path of the parts leads froma lower entry zone spirally upward to an exit zone. For moving theparts, the entire vessel containing the plating solution is made tovibrate (FR-A 2 103 611).

Since during the coating the material of the anodes is eroded anddeposited on the bulk material, the anodes must, as is known, bereplaced after a predetermined number of hours of operation. Further itis desired to obtain a high material utilization of the anodes, and inaddition the availability of the installation is to be maintained byreduction of the down times for changing the anodes.

For the electrolytic surface coating of pourable material, in particularfor the electrodeposition of aluminum in a vibrator conveyor system, theanodes may be disposed, accessible from the outside, on the inner wallof the vessel or on a so-called anode shaft cover. As the anodes areused up by the coating process, their life is limited to a predeterminednumber of hours of operation. For this reason they are replaced whenabout 50 to 70% of their material has been used up. This is necessarybecause otherwise the anodes may corrode through if the erosion isirregular and the remaining stumps may warp due to their dead weight andmay thus establish a shortcircuit to the cathode. For changing theanodes, the installation filled with electrolyte at about 100° C. mustbe cooled, emptied, flushed with toluene, and dried. The electric leadsof the anodes are disconnected, the anodes exchanged through openings inthe vessel wall, and for restarting the apparatus these operations occurin reverse order.

SUMMARY OF THE INVENTION

It is the object of the invention to indicate an apparatus forelectrolytic surface coating of bulk material with a vibrator conveyorsystem which is of especially simple design and makes simple changing ofthe anodes possible. In particular the life of the anode is to belengthened considerably.

According to the invention, this problem is solved with thecharacterizing feature of claim 1. In this form of realization of theapparatus for surface coating it is possible, after a predeterminednumber of hours of operation, to remove residual anode material from theinstallation in a simple manner and to supply new anode material as agranulate.

The cathode and anode tracks are appropriately secured on jointsupporting stringpieces which serve at the same time as power lead forthe cathode. These supporting stringpieces are then appropriatelyconnected with the central pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

For further elucidation of the invention reference is made to thedrawing, in which an apparatus for electrodeposition of aluminum isillustrated schematically as a practical example.

FIG. 1 shows a transverse section through the installation, and

in FIG. 2 the design of the electrodes and their electrical contactingis illustrated.

FIG. 3 depicts a further embodiment of the invention wherein thecathodic track is electroconductively connected to the contact bar viascrews and contact pins.

FIG. 4 depicts yet a further embodiment of the invention and illustratesa power lead.

DETAILED DESCRIPTION OF THE INVENTION

In the apparatus according to FIG. 1 for electrolytic surface coating ofpourable material, preferably for the electrodeposition of metal, inparticular aluminum, from an aprotic, oxygen- and water-freealuminum-organic electrolyte, a vibrator conveyor is provided for thetransport of pourable material to be coated. The vibrator conveyorcomprises a central pipe 2 with a bottom 3, a cover 4, and a sidewall 5.The central pipe 2 protrudes from a vessel 6, the cover 7 of which inthe form of an annular disk is fastened on the sidewall 5 of the centralpipe 2 through a flexible connection 8. The sidewall 5 of the vessel 6is connected with the bottom. The bottom 3 of the central pipe 2 rests,able to vibrate, on springs 9 and on a gas cushion 10, which is enclosedin the manner of a diving bell between the bottom 3 of the central pipe2 and an annular-cylindrical extension 11 of the central pipe 2, as wellas an electrolyte 12, by which also the central pipe 2 is partiallysurrounded. Above the electrolyte 12 a gas chamber 14 is formed, whichmay be filled preferably with nitrogen. The central pipe 2 is providedwith an oscillatory drive 16, which is disposed on a bearing block 17above the cover 4 of the central pipe 2.

In conjunction with a mechanism not shown in the figure, the drive 16produces an oscillating movement of the central pipe 2 and hence of aconveying trough containing the bulk material 20, which trough forms acathodic track 22, arranged spirally around the central pipe 2 andconnected with it. The conveying trough 21 is provided with supportingstringpieces 24 to 31, disposed at predetermined intervals around thecentral pipe 2. The supporting stringpieces 24 to 29 serve both asmechanical mount and as power lead for the cathodic track 22 and hencealso of the bulk material 20. Two additional supporting stringpieces 30and 31, present above the electrolyte 12, serve only to fasten thecathodic track 22. Each of the superposed stringpieces 24 to 26 and 27to 29 is electroconductively connected by means of a contact bar 32, 33to an electrode terminal 34, 35. For supplying the bulk material thereis provided a feed lock 38, and for the removal of the bulk material, adischarge lock 39.

Between the spirals of the conveying trough a granulate anode 40 isprovided, which consists of a granulate of the material that is intendedfor the coating of the bulk material and is transported through theoscillating movement of the central pipe 2 of a perforated anodic track42 consisting of an electrically insulating material. As power lead forthe granulate anode 40 contact pins 46 to 49 are provided. Thesuperposed contact pins 46 and 47 are connected via a contact bar 52 anda flexible connecting conductor 54 to an electrode terminal 56, which isconnected to a voltage source not shown in the figure. In like mannerthe contact pins 48 and 49 are connected via a contact bar 53 and aflexible connecting conductor 55 to an electrode terminal 57, which toois connected to a supply voltage not shown in the figure. In this formof realization of the apparatus, consumed anode material can be replacedcontinuously by new granulate during the deposition. For this purpose alock not shown in the figure is provided for supplying the anodematerial and possibly also for its removal. These locks may be offset90° for example relative to the locks 38 and 39 for the bulk material20.

In the form of realization according to FIG. 2, only a part of FIG. 1with the supporting stringpiece 25 is shown, which is fastened on thecentral pipe 2 and connected electroconductively with the contact bar32. The cathode track 21, containing the bulk material 20, is screwed tothe supporting stringpiece 21. For this purpose screws 61 are used whichconsist of electrically conducting material and which may in particularbe provided with enlarged heads. These screws, for example six for eachof the stringpieces, of which only three are indicated in the figure forsimplification, serve both for the mechanical attachment of the cathodetrack 22 on the stringpiece 25 and for current transmission from thecontact bar 32 to the cathode track 22. The stringpiece 25 iselectrically insulated against the central pipe 2. The stringpiece 25comprises a metallic contact pin 65, surrounded by a sheath 66, whichmay consist of electrically insulating material, preferably laminatedcloth. The screws 61 form an electric connection between the bulkmaterial 20 and the contact pin 65, which is electroconductivelyconnected with the contact bar 32. The granulate anode 40 is connectedvia a screw union with screws 64, which can serve both for theattachment and for the electric contacting of the granulate anode 40, tothe electrically insulating contact pin 46, which is connected to thecontact bar 52. The electrical and chemical insulation of the contactbar 52 and of the contact pin 46 is not shown in the figure forsimplification.

In a further form of realization according to FIG. 3, the cathodic track22 containing the bulk material 20 is electroconductively connected tothe contact bar 12 via screws 61 to 63 as well as contact pins 67 to 69.For the anode granulate contained in the anodic track 42, however, aseparate power lead 70 is provided, consisting of the anode granulate40. This power lead 70 consists of an insulated down pipe 72, which isfilled with the anode granulatee 40. Protruding into this anodegranulate 40 is an electric conductor 74 which is passed through thedown pipe 72 and is connected to the anode terminal 56 via the flexibleconnecting conductor 54. Admission of the granulate 40 to the power lead70 occurs through an opening, not specifically marked, in the cover 7 ofvessel 6. Above the cover 7 a lock 78 is provided, which may beconstructed in known manner and is indicated only in dash-dot lines inthe figure.

The granulate anode is moved with the vibration of the central pipe 2 inthe anode track 42 preferably in a closed loop. For this purpose theanode track may be provided for example with a return device not shownin the drawing, which may consist for example of a valve controllablefrom the outside, by means of which the anode granulate 40 falls from anupper part of the anode track 42 back onto a lower part. In similarmanner also the bulk material 20 can be conducted in a closed loop untila sufficient coating has been obtained.

In the form of realization according to FIG. 4, besides the power lead70 with the down pipe 72 and the conductor 74 there is associated withthe anodic column an additional power lead 71. In this poer lead 71,too, an anodic column is formed by the granulate, which column iscontacted by a conductor 75 protruding into the anodic column in theupper part of the down pipe 73.

What is claimed is:
 1. An apparatus for electrolytic surface coating ofa pourable material, comprising: a vibrator conveyor having a conveyingtrough serving as a cathodic track, the conveying trough being disposedspirally around a central pipe, the central pipe partially dipping intoa vessel for holding a source of electrolyte and the central pipe beingprovided with an oscillatory drive; a granulate anode associated withthe conveying trough, the granulate anode comprising a granulate of thematerial provided for the surface coating, and the granulate anode beingmovably mounted in a perforated anodic track having about equalcurvature to the cathodic track and at least substantially constantdistance from the cathodic track.
 2. The apparatus according to claim 1wherein the cathodic track is mounted on supporting stringpieces whichare fastened on the central pipe and which functions as an electricpower lead.
 3. The apparatus according to claim 1 wherein the anodictrack is fastened on supporting stringpieces of the cathodic track. 4.The apparatus according to claim 2 wherein the anodic track is fastenedon supporting stringpieces of the cathodic track.
 5. The apparatusaccording to claim 1 wherein the granulate anode has a power leadcomprising granulate of the material used for the surface coating. 6.The apparatus according to claim 2 wherein the granulate anode has apower lead comprising granulate of the material used for the surfacecoating.
 7. The apparatus according to claim 3 wherein the granulateanode has a power lead comprising granulate of the material used for thesurface coating.
 8. The apparatus according to claim 5 wherein thegranulate anode has a power lead comprising granulate of the materialused for the surface coating.
 9. The apparatus according to claim 5wherein the power lead is a down pipe which is at least partially filledwith granulate of the material used for the surface coating, theapparatus further comprising an electric connecting conductor whichprotrudes into the granulate in said down pipe and which is connected toan anode terminal.
 10. The apparatus according to claim 6 wherein thelead is a down pipe which is at least partially filled with granulate ofthe material used for the surface coating, the apparatus furthercomprising an electric connecting conductor which protrudes into thegranulate in said down pipe and which is connected to an anode terminal.11. The apparatus according to claim 7 wherein the lead is a down pipewhich is at least partially filled with granulate of the material usedfor the surface coating, the apparatus further comprising an electricconnecting conductor which protrudes into the granulate in said downpipe and which is connected to an anode terminal.
 12. The apparatusaccording to claim 5 further comprising a second power lead comprisinggranulate of the material used for the surface coating.
 13. Theapparatus according to claim 9 further comprising a second power leadcomprising granulate of the material used for the surface coating.